This invention relates to a stabilising strip for use in stabilised earth structures.
A stabilised earth structure is one in which stabilising elements, such as elongate strips, are combined with backfill, such as earth, in order to form a composite material. The strips extend rearwardly from a facing into the backfill and are horizontally and vertically spaced from each other. Such structures are commonly employed to provide retaining walls and abutments for bridges. They are known from, for example, GB-A-1 069 361 incorporated herewith by reference.
In the vast majority of cases, the stabilising elements are provided in the form of strips having a length of between about 3 and 10 m, although shorter strips and occasionally longer ones of up to about 20 m may be used. The width of the strips is generally between 4 and 6 cm although it is known to use strips of up to 10 or 25 cm in width. Their thickness ranges from about 1 mm to a few centimeters and is generally in the range of 1 to 6 mm.
The purpose of the stabilising strips is to transmit forces within the earth mass and to distribute stresses. In particular, it is firstly necessary to transmit forces between a strip and the backfill in which it is placed and therefore the strip must have a sufficiently large surface area to develop through friction the required shear resistance per unit length. In order to increase the shear resistance, the width of the strip must be increased. The surfaces of the strip may also be provided with laterally extending ribs to increase the frictional interaction with the earth, as is known from GB-A-1 563 317 incorporated herewith by reference.
Secondly, the strips must be capable of transmitting forces along their length and therefore it is necessary that they have a high tensile strength.
As well as these two main functions which are fundamental to the basic operation of the stabilised earth structure, various other characteristics are also highly desirable. A reinforcing strip should be able to flex in a vertical plane in order to accommodate soil deformation, such as settlement or shrinkage, without being damaged; the strip should have a high breaking strain, to give good elongation before it breaks; and the strip should also be durable, having a slow and predictable rate of degradation with time, even in an aggressive backfill environment. When steel strips are used, these requirements generally make it necessary to use strips of at least 4 or 5 mm in thickness in order to provide the necessary strength, bearing in mind the effects of degradation over time. When this thickness is combined with the width of the strip which is required in order to provide sufficient frictional interaction with the earth, the result is a technical over-design in terms of the tensile capacity of the strip, particularly for low structures and the upper part of higher structures. It will be appreciated therefore that strips having a high weight per unit length are employed, such that the strips are heavy to transport and install, as well as expensive.